265/35R18 vs 225/30R20

225/30R20 is 0.01 in (0.3 mm) taller than 265/35R18, a +0.05% diameter difference. With the speedometer set for 265/35R18, an indicated 60 mph is 60.0 mph on 225/30R20.

Is this a safe swap?

Diameter difference +0.05%: under 1%

By overall diameter alone, 225/30R20 is a near match for 265/35R18; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

265/35R18 vs 225/30R20 differences
Measurement	265/35R18	225/30R20	Difference	% diff
Overall diameter	25.30 in (642.7 mm)	25.31 in (643.0 mm)	+0.01 in (+0.3 mm)	+0.05%
Sidewall height	3.65 in (92.8 mm)	2.66 in (67.5 mm)	−0.99 in (−25.2 mm)	−27.22%
Section width	10.43 in (265.0 mm)	8.86 in (225.0 mm)	−1.57 in (−40.0 mm)	−15.09%
Circumference	79.49 in (2,019.1 mm)	79.53 in (2,020.0 mm)	+0.04 in (+0.9 mm)	+0.05%
Revolutions per mile	797	797	0	−0.05%

True speed with the speedometer calibrated for 265/35R18
Indicated	Actual on 265/35R18	Actual on 225/30R20
30 mph	30.0 mph	30.0 mph
60 mph	60.0 mph	60.0 mph
75 mph	75.0 mph	75.0 mph

Ride-height change: 225/30R20 raises the vehicle by 0.01 in (0.1 mm) at the axle (half the +0.3 mm diameter difference).

225/30R20 is 0.01 in taller than 265/35R18 and 40 mm narrower, a 0.05% difference in overall diameter.

With the speedometer calibrated for 265/35R18, an indicated 60 mph is actually 60.0 mph on 225/30R20, and revolutions per mile change from 797 to 797.

225/30R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 265/35R18.

Size pages

Other comparisons with 265/35R18

Other comparisons with 225/30R20

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.